The present invention relates to a hydraulic tensioning system for an endless drive, especially a chain drive of an internal combustion engine. The tensioning system comprises a housing, in which a spring-mounted piston charged by a hydraulic fluid is guided so that it can move longitudinally. The piston together with the cylinder defines the boundaries of a pressure space filled with a hydraulic fluid. For damping adjustment movements of the piston, the hydraulic tensioning system includes a damping device, in which the hydraulic fluid can be discharged from the pressure space via at least one leakage gap.
Such a tensioning system is known, for example, from DE 196 31 607 A1. In this hydraulic tensioning system, a long standstill period of the internal combustion engine can have the result that the pressure drops in the pressure space of the tensioning system, because hydraulic fluid that charges the pressure space by the pressure circulating lubrication of the internal combustion engine escapes. When the internal combustion engine is started, in the time period up to reaching the pressure build-up in the pressure space, the hydraulic tensioning system is not in the position to realize a necessary biasing of the traction drive element. Consequently, an increased noise level is produced, caused by rattling or bumping of the traction drive element or a tensioning rail connected to the traction drive element on the tensioning system. Simultaneously, increased wear is produced in the start-up phase of the internal combustion engine until reaching the pressure build-up in the pressure space.
The noise generation in the start-up phase of the internal combustion engine for the known hydraulic tensioning systems does not satisfy the demands for comfort that are placed on today's vehicles. In the operating mode, these tensioning systems exert a predetermined tension on the traction drive element via a pressurized piston. The traction drive element, especially a chain, biased in normal operation reduces or eliminates wear due to elongation and damps vibrations as much as possible, wherein these vibrations are caused by rotational irregularity in the internal combustion engine and are introduced into the endless traction drive element. The known hydraulic tensioning systems, however, are not suitable for guaranteeing a low-noise guidance of the traction drive element for a reduced or insufficient pressure of the hydraulic fluid in the pressure space as well as for high-frequency loads on the traction drive element.
The problem of the invention is to further form a hydraulic tensioning system according to the class, such that this system guarantees an effective and low-noise guidance of the traction drive element in all of the operating modes of the internal combustion engine.